This invention relates to signal processing in a radio transmitter. In particular, it relates to methods and means of compressing a voice signal before transmission and of detecting the presence of a voice signal for purposes such as controlling transmission.
Two features that are well known in transmitters designed for two-way radios are audio compression and voice-operated transmission (VOX). Audio compression is reduction of the dynamic range of a signal by applying the signal to some nonlinear circuit that reduces the magnitude of variations of power level about the average to increase the understandability of a received signal that contains noise. VOX is a well-known means of controlling the operation of a transmitter in response to a detected audio signal. The two functions are nominally independent of one another and are normally carried out by separate circuits. This becomes a disadvantage in circuits designed for very large-scale integration (VLSI). In such circuits the reliability and yield are functions of the surface area of the semiconductor chip used to make the circuit. Reliability and yield are both improved with smaller circuits. It is, therefore, an important goal of the designer to reduce the number of components and hence reduce the area of the semiconductor chip.
It is an object of the present invention to provide improved operation of a voice-operated transmitter.
It is a further object of the present invention to combine in one circuit the functions of audio compression and detection of the presence of a voice signal.
Other objects will become apparent in the course of a detailed description of the invention.